Metal oxide semiconductor (MOS) integrated circuits typically operate from a +5 volt power supply, V.sub.DD, with a second power supply forming a ground, or V.sub.SS, supply at 0 volts. In integrated circuit memories, these power supplies are each typically provided on one device pin. Each device pin is wire-bonded to a bonding pad on the integrated circuit itself. Although bond wires and package pins insert a series resistance and inductance between the bonding pad and the external power supply, it is useful to think of the power supply provided on the bonding pad as an ideal voltage source. One or more metal power supply lines are connected to each power supply bonding pad and route the power supply voltages throughout the integrated circuit. As the distance between functional circuitry and the bonding pad increases, the characteristics of the power supply provided to the functional circuitry become less ideal. Connecting to the ideal voltage source via a relatively thin metal line adds series resistance and capacitance between the connection point and the ideal voltage source. For the V.sub.SS supply, when the current, I.sub.DD, is at a peak, the voltage level on the V.sub.SS lines the most distant from the bonding pad can rise and cause the functional circuitry to malfunction.
In integrated circuits with only one device pin for a given power supply, a main metal line, typically 0.01 inches wide for a large integrated circuit memory, is used to bus the power supply to all the functional circuitry. Smaller metal lines connect to the main metal line, but the main metal line is the primary conduit for routing a power supply from one side of the integrated circuit to another. The single-pin requirement fixes a maximum length between the bonding pad and the functional circuitry on the opposite end of the integrated circuit for a given size of the main metal line. Conversely, for a given length from the farthest functional circuitry to the bonding pad, the main metal line must be at least a given width to provide a power supply adequate to ensure proper operation.
Resistance through a conductor can be determined by the following formula: EQU R=(.rho.*L)/W
where .rho. is the resistivity of the conductor, W is the width of the conductor, and L is the length of the conductor. Because of this basic relation, and since .rho. and L are fixed, the width W of the metal conduit determines whether the resistance R is low enough to prevent incorrect operation during times of peak current. A technique used in the prior art has been to increase W until R becomes low enough to ensure correct operation. A problem with this approach, however, is that W must be so large, 0.01 inches typically, that the size of the integrated circuit increases substantially due to the width of the main power bus lines. The tradeoff between W and integrated circuit size also results in a power supply that is barely good enough to avoid malfunction.